Error propagation and signal path protection in optical network

ABSTRACT

A method and a device in a cross-connector node in an optical network for error propagation and signal path protection including supervision of incoming signal on input port, switching off of output port at loss of signal, alteratively switching so that output port is connected to signal source being part of protected path, and restart respective reconnection at detection of recurred signal.

TECHNICAL FIELD

The present invention relates to error propagation and signal pathprotection in optical communication networks.

PRIOR ART

At a fiber break or at error in a laser in a static optical network, theerror will propagate through the network by itself. Transponderspropagate/transmit the error by switching off themselves when they haveno incoming light. In a completely optical network the light is notregenerated; consequently the error there will propagate in a naturalway. Thus, the loss of signal will be detectable further on along thetransmission path. If, on the other hand, there are electro-opticalcross-connectors in the network, more logic is required to make theerror propagate. The laser in a transceiver is not switched offautomatically. Besides, the signal will have its input into across-connector by one of several Rx-ports (reception ports) and itsoutput by one or more Tx-ports (transmission ports).

The aim of the present invention is to provide a method to achieve thata signal error, which has been detected in the optical network,propagates in the transmission direction, to at that make it possible tobe detected by subsequent nodes in the network and by that makeswitching off/disconnection of related transmission ports possible,alternatively achieve that related cross-connectors perform so calledprotection switching.

SUMMARY OF THE INVENTION

The invention relates to a method and an arrangement in across-connection node in an optical network including supervision ofincoming signal on input port, switching off/disconnection of outputport at loss of signal, alternatively switching so that output port isinterconnected with signal source being part of protection path, andrestart respective re-switching at detection of recurred signal.

The invention is defined in the patent claims. Preferred embodiments aredefined in the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to the figuresbelow, of which:

FIG. 1 shows a cross-connector node with control logic;

FIG. 2 shows signal propagation via a primary signal path in an opticalnetwork with a number of letter-marked nodes;

FIG. 3 shows the network in FIG. 1 inclusive a protection signal path;and

FIG. 4-8 show error propagation and events if an error occurs.

FIG. 4:

A=An error occurs, i.e. the laser fails in node c, or the fiber betweenc and d is broken/cut. Signal detection at input port of node d detectsloss of signal.

FIG. 5:

B=Propagate the error, i.e. find laser to which input port is connectedand switch off.

FIG. 6:

C=Propagate the error, i.e. find laser to which input port is connectedand switch off.

FIG. 7:

D=Propagate the error, i.e. find laser to which input port is connectedand switch off.

FIG. 8:

E=This is the last node in the path. Perform cross-connection toprotection path. Don't switch off the laser!

FIG. 9 shows a cross-connector node and control logic according to oneembodiment of the invention;

FIGS. 10 a-d and 11 show a flow chart for a method according to onepreferred embodiment of the invention.

FIG. 10 a:

A=Input signal lost/lacking ?

B=Initiate timer

C=Store input port ID

D=Store output port ID

E=Timer period expired ?

F=Input signal still lost/lacking ?

G=Output port is end port in protected path

H=Connect input port from protected path to output port

I=output port is part of protected path ?

J=switch off output port (i.e. the laser)

FIG. 10 b:

K=Output port is end port in primary path ?

L=Output port is part of primary path ?

M=Switch off output port (i.e. the laser)

FIG. 10 c:

N=Signal back ?

O=Initiate timer

P=Timer period expired ?

Q=Signal still on/in existence ?

R=Output port is end port in protected path ?

S=Connect input port from protected path to output port

T=Output port is part of protected path ?

U=Switch on output port (i.e. the laser)

FIG. 10 d:

V=Output port is end port in primary path ?

W=Output port is part of primary path ?

X=Switch on output port

FIG. 11:

A=Start. Input Port is the input port which is connected to this OutputPort. Prot. Port is defined if this is end port in primary path.

B=Input signal not existing/lacking from input port ?

C Initiate timer

D=Timer period expired ?

E=Input signal not existing/lacking from input port ?

F=This output port is end port in primary path

G=Connect input port from protection path to output port (connect Prot.Port to Output Port)

H=This output port is part of primary path ?

I=Switch off laser of Output Port

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to error detection and signal errorpropagation in networks with opto-electrical cross-connectors where onewants to have the possibility to propagate loss of signal and possiblyperform 1+1-protection. The invention includes a method to detect lossof signal at inputs to cross-connector nodes, transmission of loss ofsignal to outputs of cross-connector nodes, and decision method andcontrol method for performing of protection switching for protectedsignal paths.

One preferred embodiment is described here with reference to FIG. 1.FIG. 1 shows a cross-connector node 101 with a control logic 120 whichis connected to and controls a number of input ports 110 and a number ofoutput ports 140. Between the input ports 110 and the output ports 140,a switch matrix 130 is arranged which also is connected to the controllogic and which makes possible that just any input port can be connectedto just any output port, controlled from the control logic 120. In thecase that a signal on an input port 110 disappears, this dropout isdetected and the control logic 120 in the cross-connector node 101checks which output port/ports 140 that are interconnected with saidinput port 110 in the switch matrix 130, and switches off these outputports 140, or alternatively performs protection switching.

The function is shown in the example in FIGS. 2-8.

FIG. 2 shows a primary signal path 210 which extends over the nodesa-c-d-j-l-m. FIG. 3 shows a redundant signal path 310 which extends overthe nodes a-b-f-g-i-n-m; the first node a) transmits the signal bothpaths, that is, both to node b) and node c). The fact that a redundantsignal path has been established results in that the primary path iscalled protected path.

FIG. 4 shows what will happen if an error occurs on the path betweennode c) and node d). The error can, for instance, consist of that thetransmitter laser in node c) fails, or that the optical fiber betweennode c) and node d) is cut/broken. A signal detection unit at input portin question at node d) detects the occurred loss of signal.

FIG. 5 shows how one embodiment of the invention by its influencein/effect on node d) propagates the error to the signal path betweennode d) and node j), that is, the transmitting laser which is connectedto the input port which receives signal from node c) has been switchedoff.

FIG. 6 shows how one embodiment of the invention by its influencein/effect on node j) propagates the error to the signal path betweennode j) and node l).

FIG. 7 shows how one embodiment of the invention by its influencein/effect on node l) propagates the error to the signal path betweennode l) and node m).

FIG. 8 shows how one embodiment of the invention by its influencein/effect on node m) detects the propagated error in the primary signalpath 210 and instead connects signal from the protection path via thenode n); transmitting laser is not switched off.

One arrangement according to one embodiment of the invention includes aset of units as below and should best be implemented as a computerprogram or in hardware, or as a mixture of them.

With reference to FIG. 9, a cross-connector node according to oneembodiment of the invention is described. Each input port 910 isequipped with a signal detector 920, intended to detect existence ofsignal respective loss/lack of signal. Each signal detector is connectedto a common control logic 930. The control logic is further connected toa number of timers 941-944, one for each input port. Further, thecontrol logic is connected to an error port memory 950 for storing ofidentification code for the input ports which have a detected loss ofsignal and for storing of identification code for the output ports whichare connected to these input ports with detected loss of signal. Eachinput port and each output port is connected to a switch matrix 960 inknown way.

At operation of a device according to the invention the following stepsare run through:

-   -   signal supervision of incoming signal on input port 1010,    -   initiation of a timer at loss of signal 1012,    -   storing of identification code for input ports with detected        loss of signal 1014,    -   storing of identification code for output ports connected to        input ports with detected loss of signal 1016,    -   supervision of time for loss of signal (control of timer) 1020    -   switching, at during specified time remaining loss/lack of        signal, of protection input port to output port, if output port        is end port in protected path 1024, 1026.    -   switching off, during certain time remaining loss of signal, of        output port, that is laser, if output port is part of protected        path 1030, 1032,    -   re-connection of input port being part of protected path to        output port if output port is end port in protected path, at        recurrence of signal from input port 1050-1060, and    -   switching-on of switched off laser when signal has recurred a        certain smallest period of time 1050-1056, 1062, 1064,        1017-1074.

One preferred embodiment of the error detection of the cross-connectornode is shown by the following algorithm:

Array: TXArray

Time-out-period: TIME

Rx-port: Rxn

Rx-port: Protection-Rx

1. “Signal Detect” (SD) for RXn high

2. Wait for SD low

3. Detection of loss of signal (SD low in Rxn-port)

4. Initiate timer

5. Tx-ports connected to Rxn-port with detected loss of signal−>TXArray

6. If loss of signal unchanged during a certain period of time TIME:

-   -   a. For each Tx-port in TXArray:        -   i. if Tx-port is end port in protected path (that is,            primary path)            -   1. connect protection Rx-port to Tx-port        -   ii. otherwise if Tx-port is part of protected path            -   1. switch off Tx-port (laser) so that the error                propagates

7.

-   -   a. Wait for SD high    -   b. SD high detected on Tx-port    -   c. Initiate timer    -   d. If SD high unchanged during a certain period of time TIME:        -   i. for each Tx-port in TXArray:            -   1. if each Tx-port is end port in protection path:                -   a. connect Rxn-port to Tx-port            -   2. otherwise if Tx-port is part of protection path:                -   a. switch on Tx-port (laser) so that the signal                    propagates

8. Return to (1)

1. Method for error detection and signal path protection in opticalcommunication networks comprising cross-connector nodes with input portsand output ports having lasers, comprising the following steps:supervision an detection of signal loss of an incoming signal on inputport of cross-connector node, switching off/disconnection of the outputport connected to said input port of the cross-connector at said loss ofsignal in the case the output port is part of protected path, whereinsaid disconnection of said output port comprises disconnection of thelaser of said output port and in the cross-connector node, connection ofprotection input port to the output port at said loss of signal in thecase the output port is end port in protected path.
 2. Method as claimedin claim 1, further including the step of: in said cross-connector node,disconnection of the output port connected to said input port at saidloss of signal in the case the output port is an end port or a part ofan unprotected primary path.
 3. Method as claimed in claim 2, furtherincluding the steps of: in said cross-connector,reconnection/re-switching of input port being part of protected path tooutput port in the case said output port is end port in protected pathand the signal at said input port has recurred, switching on of switchedoff laser in the case the signal at the input port being part of primarysignal path has recurred.
 4. Cross connector node for an opticalcommunication network, comprising input ports, output ports havinglasers and a switch matrix, and signal detectors at each input portwhich detects loss of signal, if any, and communicates the loss ofsignal via one or more connections to a control logic, said controllogic being connected to switch matrix and output ports and is devisedwith means for switching off the lasers of said output ports.
 5. Deviceas claimed in claim 4, further comprising a set of timers connected withthe control logic and intended to be started at loss of signal andsignal to the control logic when this loss of signal has been the statefor a certain period of time.
 6. Device as claimed in claim 5 furthercomprising an error port memory connected to the control logic andintended to store information about which output ports that areconnected to input ports with detected loss of signal.